How to load CPU microcode in Debian?

Question

How do you do that, e.g. for microcode_amd_fam15h.bin?

What is in /lib/firmware/amd-ucode?

Answer 1

First, you should install the amd64-microcode package using the package manager.

It will provide the /lib/firmware/amd-ucode/microcode_amd_fam15h.bin file for you (and also other microcode files for other AMD processor families).

It will also provide the script /usr/share/initramfs-tools/hooks/amd64_microcode, which will run as part of any update-initramfs -u operation, to add the microcode and the procedure to feed it into the CPU as early in the boot process as possible. Installing the amd64-microcode package will probably run update-initramfs -u for you automatically.

If you need more information, you might want to read the files in /usr/share/doc/amd64-microcode/ (after installing the amd64-microcode package). Here's a web copy of the main README file as it currently exists on the stable Debian 11.

If you need to use a different version of the microcode for any reason (e.g. you have a problem and need to verify with an older microcode, or have a newer microcode and the Debian package has not yet been updated), you should just overwrite the packaged /lib/firmware/amd-ucode/microcode_amd_fam15h.bin with the desired microcode version, run update-initramfs -u and then reboot.